I think it's an AT&T thing perhaps. With me, two sounds can happen when a call disconnects and it depends on whether you disconnent first or not. If you disconnect first, you get a boop sound (best way to describe it). It's a little on the loud side but generally tolerable to me. However, when the other person disconnects first I immediately get a three tone sound. It's the error sound for a failed call. And on my AT&T berry it is quite the ear piercer if you don't get to the end call button quick enough.